The expression of water- and oil-repellency results from the low surface energy of fluorine, and, usually, fluorine-containing acrylate polymers are widely used as active ingredients of water- and oil-repellents. Previous various investigations have shown that the presence of crystallinity in a fluorine-containing polymer is necessary for expressing water- and oil-repellency in practical applications. In particular, it has been recognized that the hydrophobicity of a fluorine-containing polymer depends on the number of carbon atoms of a side-chain fluoroalkyl group and that the expression of crystallinity is observed when the number of carbon atoms is eight or more.
[Non-Patent Document 1] Secchaku (Adhesion), Vol. 50, No. 5, pp. 16-22 (2006)
Therefore, it has been regarded that a fluorine-containing polymer having a short fluoroalkyl group, i.e., a side-chain fluoroalkyl group having 7 or less, in particular, 6 or less carbon atoms, is low in or does not have crystallinity and thereby cannot provide water-repellent performance that is sufficient for practical use. In addition, since water- and oil-repellents are required to have washing resistance and abrasion resistance, fluorine-containing acrylic polymers having long side chains are used.
However, polymers including a side-chain fluoroalkyl group having 8 or more carbon atoms are very hard due to their high crystallinity and have a problem that flexibility of textile products is impaired. Furthermore, since the water-repellent process needs high curing temperature, there are problems such as a change in color of fibers. In addition, since the polymers including a long side-chain fluoroalkyl group having 8 or more carbon atoms are excessively hydrophobic, a large amount of an emulsifier is necessary for producing a water- and oil-repellent.
The present applicant has before proposed a water- and oil-repellent composed of an aqueous emulsion in which a copolymer of a fluoroalkyl group-containing polymerizable monomer and vinylidene chloride or benzyl(meth)acrylate, and a carboxyl group-containing water-soluble polymer are dispersed in water using a nonionic surfactant. The fluoroalkyl group of a fluoroalkyl group-containing polymerizable monomer that is copolymerized with vinylidene chloride or benzyl(meth)acrylate is recognized to be a perfluoroalkyl group having 4 to 20 carbon atoms, but the perfluoroalkyl group used in the above-mentioned polymerization example is recognized to be a mixture of perfluoroalkyl groups having 6 to 14 carbon atoms, 9.0 on average.
[Patent Document 1] JP-A-11-80710
Accordingly, it is believed that a water- and oil-repellent showing excellent in flexibility and also excellent in washing resistance can be obtained if water- and oil-repellency can be expressed with a fluorine-containing polymer including a short side-chain fluoroalkyl group having 6 or less carbon atoms.
It has been also proposed a surface-treating agent showing excellent water repellency, oil repellency, and antifouling property by using a polymer having a short fluoroalkyl group having 1 to 6 carbon atoms as the side chain, but the fluoroalkyl group-containing monomer used therein is a fluorine-containing monomer compound represented by the general formula:Rf—Y—O—CO—CX═CH2                 X: F, Cl, Br, I, CFX1X2, CN, a fluoroalkyl group having 1 to 20 carbon atoms, benzyl group, or phenyl group,        Y: an aliphatic group having 1 to 10 carbon atoms, an aromatic or alicyclic group having 6 to 10 carbon atoms, a CH2CH2NR1SO2 group, or a CH2CH(OY1)CH2 group, and        Rf: a fluoroalkyl group having 1 to 6 carbon atoms.Acrylic acid derivatives in which X is H are shown as comparative manufacturing examples, and methacrylic acid derivatives in which X is CH8 are intendedly excluded.        
[Patent Document 2] JP-A-2004-352976
Furthermore, it has been proposed a water- and oil-repellent composition of which essential component is a copolymer containing as a polymerization unit (a) an Rf group-containing monomer of which homopolymer does not have a melting point derived from the Rf group in the microcrystals or has a melting point of 55° C. or less and has a glass transition point of 20° C. or more and (b) an Rf group-free monomer having a cross-linkable functional group, wherein the composition can impart excellent water- and oil-repellency to products, even in low temperature treatment, and also can perform a water- and oil-repellent process with providing soft textile feeling and also excellent durability.
[Patent Document 3] WO 2004/035708
In the above, a perfluoroalkylalkyl(meth)acrylate is used as the component monomer (a), but a specific monomer, such as a 2-butanone oxime adduct, pyrazole adduct, or ε-caprolactam adduct of a ω-isocyanate alkyl(meth)acrylate, is used as the component monomer (b) in the copolymerization reaction.